A large number of RNAs are not diffusely distributed in the cytoplasm, but are actively transported to various subcellular sites. After reaching their final destinations, localized RNAs are translated, thus directing local protein production. While increasing numbers of localized RNAs are being identified, the functional importance of these events is not well understood. We are focusing on a localization pathway that we have identified, which targets a number of RNAs to the tips of cellular protrusions. We have found that an important component of this pathway is the tumor-suppressor protein Adenomatous Polyposis Coli (APC) whose mutation is the initiating event in the progression of the majority of colorectal cancers. APC associates with RNAs at cellular protrusions in ribonucleoprotein complexes, which we term APC-RNPs. In our recent work we have found that localization of these RNAs is required for efficient cell migration and invasion. Furthermore, we have discovered that the stiffness of the extracellular matrix promotes localization of APC-RNPs and we have delineated the underlying mechanism. Specifically, we found that increased stiffness of the extracellular environment promotes actomyosin contractility, which in turn enhances formation of a specific class of detyrosinated microtubules. These stable microtubules are required for localization and/or anchoring of APC-RNPs at protrusions. Given that the stiffness of the extracellular environment promotes various aspects of metastatic behavior, we are currently focusing on testing whether the mechanism we have uncovered is involved in promoting migration of metastatic cells. An additional component of APC-RNPs is the RNA-binding protein FUS/TLS. FUS belongs to a group of prion-domain containing proteins which exhibit the property of condensing to form liquid-demixed phases, which appear to underlie the formation of various membrane-less compartments in the nucleus and cytoplasm. In the case of FUS, mutations linked to Amyotrophic Lateral Sclerosis (ALS) promote its propensity to form such types of cytoplasmic inclusions. We have been focusing on understanding how formation of these cytoplasmic inclusions impacts on localization and function of APC-RNPs. We have previously shown that ALS-associated mutants of FUS mislocalize APC-RNPs and misdirect their translation. In our more recent work we have shown that the mechanism through which FUS inclusions affect RNA localization is indirect and involves a novel function of the kinesin-1 motor protein. Specifically, we find that kinesin-1 has a novel role in promoting formation of detyrosinated microtubules through targeting the tubulin carboxypeptidase activity. In the presence of FUS inclusions, both the kinesin-1 mRNA and the kinesin-1 protein become sequestered within FUS inclusions. This prevents efficient formation of detyrosinated microtubules leading to mislocalization of APC-RNPs. These findings reveal a novel mechanism regulating the microtubule cytoskeleton which could be a contributing factor in ALS neurodegeneration. We are additionally interested in investigating any contribution of this novel pathway in cancers containing translocations of the FUS gene.